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Hawaiian Islands Synoptic Discussion and Guidance

295
FXHW60 PHFO 301958
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
948 AM HST SUN AUG 30 2015

.SYNOPSIS...
THE LIGHT TO MODERATE TRADES WILL CONTINUE TODAY WITH SHOWERS
FAVORING WINDWARD AND MOUNTAIN AREAS. A FEW AFTERNOON SHOWERS MAY
DEVELOP OVER INTERIOR LOCATIONS. HURRICANE IGNACIO IS FORECAST TO
PASS BY JUST TO THE NORTHEAST AND NORTH OF THE STATE MONDAY THROUGH
WEDNESDAY...ACCOMPANIED BY BREEZY AND WETTER WEATHER OVER THE
ISLANDS. HOWEVER...ONLY A SMALL CHANGE IN THE TRACK OF IGNACIO COULD
BRING STRONG WINDS AND MORE WIDESPREAD HEAVY RAINS ACROSS PARTS OF
THE ISLAND CHAIN. ONCE IGNACIO MOVES AWAY FROM THE ISLANDS...
DECREASING SOUTHERLY WINDS AND SCATTERED SHOWERS ARE EXPECTED FOR
THE LATER PART OF THE WEEK.

&&

.DISCUSSION...
SHOWERS HAVE BEEN MOVING ACROSS MOST NE AND WINDWARD BIG ISLAND
AREAS DURING THE MORNING HOURS...BRINGING LIGHT TO MODERATE RAIN...
ESPECIALLY FROM LAUPAHOEHOE TO HAWI. SHOWERS WERE ALSO DEVELOPING
OVER THE WINDWARD SLOPES OF HALEAKALA IN MAUI...WITH GENERALLY
WIDELY SCATTERED SHOWERS BEING OBSERVED ELSEWHERE ACROSS THE ISLAND
CHAIN.

MODELS DEPICT A ROBUST SFC HIGH PRESSURE CENTERED FAR N OF THE
ISLANDS...WHICH SHOULD KEEP A LIGHT TO MODERATE TRADE WIND REGIME
IN PLACE TODAY. MEANWHILE...POWERFUL HURRICANE IGNACIO WAS LOCATED
ABOUT 400 MILES E OF HILO AS OF 9 AM HST...MOVING NNW AT 9 MPH.

THE AIR MASS ACROSS THE ISLANDS REMAINS HUMID WITH SOUNDING PWAT
VALUES STILL ABOVE AVERAGE...1.76 INCHES ON HILO AND 1.89 INCHES ON
LIHUE. HOWEVER...LATEST INFRARED AND WATER VAPOR SATELLITE DATA
SHOWS RIDGING ALOFT WHICH WILL HELP IN KEEPING THE AIR MASS
RELATIVELY STABLE WITH WEAK INVERSIONS AROUND 7 TO 9 THOUSAND FEET.

PASSING TRADE SHOWERS WILL CONTINUE TODAY...FAVORING WINDWARD AND
MAUKA AREAS. THEN THE FORECAST BECOMES MORE UNCERTAIN AS HURRICANE
IGNACIO MOVES CLOSER TO THE STATE ON MON AND TUE. LATEST FORECAST
TRACK FROM THE CENTRAL PACIFIC HURRICANE CENTER IN HONOLULU KEEPS
IGNACIO ON A FAIRLY STEADY NW MOTION...WITH THE CENTER PASSING ABOUT
A COUPLE HUNDRED MILES TO THE NE OF THE MAIN HAWAIIAN ISLANDS
MON THROUGH WED. HOWEVER...ANY CHANGES ON THIS SCENARIO COULD BRING
THE HURRICANE CLOSER TO THE ISLANDS...WHICH WOULD TRANSLATE IN MORE
SIGNIFICANT WEATHER IMPACTS. FOR NOW...EXPECT MODERATE TO LOCALLY
BREEZY CONDITIONS FOR MON...ALONG WITH A RATHER WET WEATHER PATTERN
AS THE HURRICANE PASSES BY TO THE NE OF THE BIG ISLAND. FOR THE
LATEST DETAILS ON HURRICANE IGNACIO...PLEASE CONTINUE TO MONITOR THE
LATEST PRODUCTS FROM THE CENTRAL PACIFIC HURRICANE CENTER.
ALSO...FOR ANY AREA UNDER A TROPICAL STORM WATCH OR WARNING...PLEASE
REFER TO THE LATEST HURRICANE LOCAL STATEMENTS ISSUED BY WFO
HONOLULU.

BY MID WEEK...THE PRESENCE OF IGNACIO WILL BLOCK THE TRADE WIND
FLOW...BRINGING A GENERALLY WEAK S FLOW ACROSS MOST OF THE ISLAND
CHAIN THROUGH THE END OF THE WORK WEEK. THE GLOBAL MODELS SHOW A
SWATH OF DEEP TROPICAL ASSOCIATED WITH THE CIRCULATION OF IGNACIO
EXTENDING SOUTHWARD FROM IGNACIO AND ACROSS THE ISLAND CHAIN. THIS
PATTERN WILL FAVOR ENHANCED SHOWERS...ESPECIALLY WITH DEVELOPING SEA
BREEZES DURING THE AFTERNOON HOURS. THESE SHOWERS COULD AFFECT
NORMALLY DRY LEEWARD AREAS AT TIMES. SOME LOCALLY HEAVY DOWNPOURS
WILL BE A POSSIBILITY AS WELL.

&&

.AVIATION...
GENTLE TRADE WINDS WILL CONTINUE TO CARRY SCATTERED SHOWERS ONTO
WINDWARD SLOPES AND COASTS. LOCALIZED SEA BREEZES WILL ALLOW FOR
THE DEVELOPMENT OF AFTERNOON AND EVENING SHOWERS OVER ISLAND
INTERIORS. EXPECT ISOLATED MVFR CIGS IN PASSING SHOWERS OTHERWISE
VFR CONDITIONS WILL PREVAIL ALL AREAS. NO AIRMETS ARE CURRENTLY IN
EFFECT AND NONE ANTICIPATED.

&&

.MARINE...
A SMALL CRAFT ADVISORY IS NOW IN EFFECT FOR THE WINDWARD WATERS OF
KAUAI AND OAHU...INCLUDING THE KAIWI AND THE KAUAI CHANNELS...
THROUGH TUESDAY AFTERNOON AS SEAS CONTINUE TO INCREASE AHEAD OF
HURRICANE IGNACIO. LARGE AND DANGEROUS SURF CAN ALSO BE EXPECTED
BEGINNING FIRST ON THE BIG ISLAND...THEN SPREADING UP THE ISLAND
CHAIN DURING THE NEXT COUPLE O DAYS. A HIGH SURF WARNING REMAINS IN
EFFECT FOR THE EAST FACING SHORES OF THE BIG ISLAND...AS WELL AS A
SURF ADVISORY FOR EAST FACING SHORES OF MAUI. THIS ADVISORY MAY NEED
TO BE UPGRADED TO A WARNING LATER ON. ADDITIONAL HIGH SURF
ADVISORIES OR WARNINGS MAY BE NEEDED DURING THE NEXT FEW DAYS FOR
THE OTHER ISLANDS.

A TROPICAL STORM WARNING REMAINS POSTED FOR THE BIG ISLAND WINDWARD
AND SOUTHEAST WATERS...WITH A TROPICAL STORM WATCH POSTED FOR SOME
OF THE WATERS AROUND MAUI COUNTY. WHILE IGNACIO IS CURRENTLY
FORECAST TO TRACK JUST TO THE NORTHEAST AND NORTH OF THE COASTAL
WATERS MONDAY THROUGH WEDNESDAY...ONLY A SMALL CHANGE IN THE TRACK
OF IGNACIO COULD BRING TROPICAL STORM FORCE WINDS INTO PARTS OF THE
AREA...PARTICULARLY IN THE WINDWARD WATERS.

FOR MORE DETAILS REGARDING SURF AND MARINE IMPACTS FROM HURRICANE
IGNACIO...PLEASE REFER TO THE LATEST HURRICANE LOCAL STATEMENTS...
COASTAL HAZARD MESSAGES AND MARINE WEATHER MESSAGES ISSUED BY WFO
HONOLULU.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
TROPICAL STORM WATCH FOR MOLOKAI-LANAI-KAHOOLAWE-MAUI-BIG
ISLAND.

HIGH SURF WARNING UNTIL 6 PM HST TUESDAY FOR SOUTH BIG ISLAND-
BIG ISLAND NORTH AND EAST.

HIGH SURF ADVISORY UNTIL 6 PM HST TUESDAY FOR MAUI WINDWARD WEST-
WINDWARD HALEAKALA-LEEWARD HALEAKALA.

TROPICAL STORM WATCH FOR MAUI COUNTY WINDWARD WATERS-ALENUIHAHA
CHANNEL.

TROPICAL STORM WARNING FOR BIG ISLAND WINDWARD WATERS-BIG ISLAND
SOUTHEAST WATERS.

SMALL CRAFT ADVISORY UNTIL 6 PM HST TUESDAY FOR KAUAI NORTHWEST
WATERS-KAUAI WINDWARD WATERS-OAHU WINDWARD WATERS-KAIWI CHANNEL.

&&

$$

DISCUSSION/MARINE...REYNES
AVIATION...BEDAL